One-sentence summary: A quick, slightly dated book aimed primarily at hospital staff, clergy, and social workers who care for terminally-ill patients and their families, on how to approach the subject and emotional impact of death.
This was written in 1969, when apparently patients with terminal malignancies weren't routinely given full information or included in the decision-making about their care (next of kin was often consulted first). So one of the big messages, "Inform your patients of their condition in a frank but not hopeless manner," is old hat now. But I suspect that Kubler-Ross's thoughts were ground-breaking at the time, and the book may be one reason we have informed consent laws now. She seems to have contributed a lot to the culture of talking openly with patients about their condition, care, and ultimately their needs while dying.
On Death and Dying is meant to offer practical guidelines to caregivers on how to listen well to patients and adapt to their needs. Pretty simple, good stuff. Since it's geared toward hospital workers, the presumption is that the patient will die in the hospital, so hospice home care is not addressed. I think later on Kubler-Ross moved politically toward promoting hospice as the preferred way to die.
This is the book in which Kubler-Ross first outlined the five stages of grief: denial, anger, bargaining, depression, and acceptance. She's careful to say they won't necessarily be experienced in that order for each individual, and some stages may be repeated. It's written mostly in interview format, with patients who exemplify the points Kubler-Ross is making.
I can see that this was an important book when it was written. She took the project up when she noticed that there were no classes on death and dying at the medical school of the University of Chicago. In fact, it seems to have influenced the industry and culture of health care so well that the material is now dated.